1. Field Of the Invention
The present invention is directed to an aerator, and more particularly, an aerator for oxygenating a live bait well.
2. Description of the Related Art
When fishing from a boat, it is a common practice to bring along bait fish in tanks known as live wells. In order to keep the bait fish alive for many hours, an aerator is provided to replenish the oxygen in the water as it is depleted by the bait fish. Several distinct types of aerators have been developed.
For example, U.S. Pat. No. 3,822,498 teaches an aerator for a live well wherein water is sucked through a pump and sprayed out a distributor manifold in the form of small jets above the surface of the water. As the jets pass through the air and then strike the surface of the water, the water picks up oxygen. These systems are, however, disadvantageous for a number of reasons.
First, it is inevitable that jets of water will strike the fish and wash away the mucus outer coating which protects the fish. Second, energy consumption is high. Third, while the surface area of the live well may be aerated, the lower reaches of the bait well are not aerated, particularly when a large number of bait fish are kept in the bait well. Finally, aeration efficiency is relatively low, so that the total number of bait fish which can be kept in the well is correspondingly limited.
U.S. Pat. No. 5,321,789 teaches a bait container wherein an aeration pump causes air to bubble up from the bottom of the container to thereby aerate the water. The aerator utilizes a conventional pump, such as a piston or a diaphragm-type pump, as is well-known in the art. The amount of oxygen actually dissolved in the water by this system is, however, severely limited.
U.S. Pat. No. 5,139,659 teaches an air-lift water pump, aerator and filter. Pressurized air is supplied to the bottom of a manifold at which point the air is broken to small bubbles by a bubble reducer. These bubbles travel up a water-lift tube, bringing along entrained water. The water thus moved passes over a filter and recirculates to the tank. This system is suitable for the long-term maintenance of a small number of fish, but is unsuitable for the short-term maintenance of a large number of fish.
A further type of well-known aerator employs a motor driven propeller near the surface of the water. The propeller may be directed upwardly to cause water to be sprayed upwardly, or the propeller may be directed downwardly to cause air to be drawn under water. This type of aeration is inefficient in that a large amount of mechanical energy is required, and oxygenation occurs mainly only near the water surface. Recently a variation on this propeller type of aerator has been developed. The aerator comprises a motor mounted above the water, a downwardly directed propeller below the surface of the water, an air tube between the surface of the water and the propeller, and a shaft connecting the propeller to the motor and extending through the air tube. As the propeller spins, it creates a suction at the bottom of the air tube, and an air stream is drawn down through the air tube whereupon it contacts the propeller and is broken into small bubbles. This aerator is intended to facilitate drawing air down to a deeper depth, and represents an improvement over the conventional propeller aerator in that oxygenation will occur at lower levels of the bait well. However, the arrangement requires the propeller to create suction on the air tube at the propeller depth. As result, the arrangement is effectively limited to shallow depths and relatively small bait wells such as minnow buckets. A further improvement is needed.
U.S. Pat. No. 4,917,577 teaches a high speed centrifugal oxygenator including (1) a frustro-conical shaped impeller chamber within which is mounted a similarly shaped mismatched impeller with blades significantly smaller than the chamber, the impeller chamber having a bottom inlet, and the bottom inlet having a venturi gas inlet for mixing gas with the flowing liquid. To be effective, the impeller must operate at very high speed in order for the flow of fluid through the bottom inlet to be sufficient to create a suction on, and draw gas through, the venturi gas inlet. This high flow rate would render the oxygenator impractical for use in small applications such as bait wells, since the high turbulence would be injurious to the bait fish. More importantly, since the impeller blades are significantly smaller than the impeller chamber, most of the fluid does not come into contact with the blades. This may be desirable where the objective is to achieve high flow, low agitation. However, where the object is to achieve a high rate of mixing of air into a relatively small volume of water, as would be required in a bait well application, this high speed centrifugal oxygenator is entirely unsuitable. Finally, the venturi gas inlets must be narrow to be effective as the pump is cycled through many ON-OFF periods, during which the venturi gas inlets will be flooded and dried, flooded and dried, resulting in sedimentation and encrustation. The venturi jets will require attention and cleaning over time.
U.S. Pat. No. 4,994,177 teaches a bait well wherein a pump, such as a bilge pump, is used to pump water up above the surface of the water and back down onto the water in the form of fine jets to thereby oxygenate the water. However, as discussed above, the oxygenation efficiency is low and the jets of water spraying on the bait fish are injurious to the bait fish.
U.S. Pat. No. 5,077,932 teaches a water aeration apparatus including a shaft driven, downwardly directed propeller located below the surface of the water, and an airway tube for delivering small amounts of air to an onlet on the top of the water intake side of the downwardly directed propeller. Rotation of the propeller draws water from the airway outlet and disperses the air into the water. This system is satisfactory for the short-term housing of a limited number of bait fish in a bait bucket. However, a significant improvement in oxygenation efficiency is needed where it is desired to house a significant number of bait fish in a live well.
Finally, U.S. Pat. Nos. 5,213,718 and 5,275,762 teach aerators wherein an impeller draws a water and air mixture down through an upwardly directed impeller inlet into a cavitation zone (i.e., the centrifugal pump is mounted upside down compared to the normal operating position). When the centrifugal pump rotates, the vacuum formed in the cavitation zone by rotation of the impeller will draw air through the air tube into the cavitation eye where a portion of the air will be entrained in the water flowing through the vaned impeller and out the water flow directing means into the tank. Excess air drawn into the cavitation eye through the inlet tube can escape upwardly through the water inlet thereby preventing air locking of the impeller, as would occur if air were to accumulate in the cavitation zone of a centrifugal pump mounted in the "normal" pump operating position, with the water inlet opening downwardly. The pump preferably floats on the water with the air/water inlet for the centrifugal pump immediately below the surface. Such a system has a number of attendant problems. First, a centrifugal pump is designed to be operated in a certain orientation. The pump may be operated upside down near the surface for periods of time without damage; however, if operated upside down at depth for any length of time, air in the motor housing will exit through the seal between the motor shaft and the impeller, and water will enter the motor housing causing damage. Further, if the pump is operated on the surface, oxygenation of the water will occur near the surface of the tank, and the lower reaches of the bait well will not be aerated.
Further yet, if the pump is operated at depth, the design must permit escape of excess air out through the water inlet so as to prevent air locking of the pump, or to permit flooding and restarting of an air-locked pump. The design must thus anticipate the various depths at which the pump may be operated, and the air-escape parameters for each depth. Such a design can not optimize the air/water mixture for maximum oxygenation of the pump at every given depth. As a result of these design constraints, the oxygenation efficiency is adequate, but much less than optimal.
What is needed is an aerator which delivers optimal oxygenation at any given depth of operation. Further, the aerator pump must operate in the orientation for which it was designed. Further, the aerator must operate at a depth where mechanical churning forces are optimal. Finally, what is needed is an oxygenator which can deliver two to four times the amount of dissolved oxygen to a given volume of water per amp.
In view of the foregoing, it is an object of the present invention to provide an aerator which eliminates or minimizes the above-mentioned and other problems, limitations and disadvantages typically associated with conventional aerators, and to provide an aerator which achieves a high level of oxygenation of the water in a live well and thereby makes possible the keeping of a larger number of bait fish per unit space than hitherto considered possible.
It is a further object of the invention to provide an aerator which has a gentle action and does not harm the bait fish.
It is yet a further object of the invention to provide an aerator which is highly energy-efficient and thus does not consume unnecessary electricity, is compact, simple to manufacture, easy to install and use, inexpensive, and reliable.